Effect of Skew Angle on Bridge Superstructures

In this paper, the effect of skew angle on reinforced concrete skew bridge decks is presented by using the grillage analogy. The actual deck system of the bridge is represented by an equivalent grillage of longitudinal and transverse beams. A span 26m of simply supported bridge deck is taken as the case study to obtain the values of the bending moment' s distribution versus span length for the one type of skewness and the results are compared against the moments of the right deck span of the bridge. The analysis results were based (BS5400) dead and live loads using Structural Analysis program (SAP2000). The analysis provided useful information about the variation of moments and shear forces with respect to change in skewness. It is concluded that in skew bridge deck, the bending moment is decreased, but torsional moments and shear forces are increased by increasing the skew angle. It is noticed that the maximum bending moment at skew angle 55o, by 76% in comparison with zero skew angle. On the other hand the maximum torsional moment increases for the same skew angle (55o) more than five times than with zero skew angles.

A Near Zero Skew Actuation Mechanism for Hard Disk Drives

One of the issues in VCM rotary actuation in hard disk drives (HDDs) is the excessive sensitivity of the system to the skew angle. The rotation of the VCM from the inner diameter (ID) to the outer diameter (OD) of the disk results in an angle of skew between the read/write head and the track. The difference in skew angle, between the ID to the OD can be as large as 25 to 30 degrees in conventional 3.5″ and 2.5″ HDDs. A large skew angle affects the slider’s flying performance and off-track capability, causing an increase in side reading and writing, and thus reduces the achievable recording density. Large skewed actuation also complicates the position error signal calibration process in the hard disk drive servo loop. This paper presents a 4 link mechanism which can be designed to achieve near zero skew actuation in hard disk drives. The profiles of the arm, suspension, and links can be designed and optimized such that the skew angle is close to zero while the VCM actuator rotates from the ID to the OD. Study shows that the 4-link mechanism does not degrade the resonance performance along the tracking direction compared to a conventional actuator.

STATISTICAL TIMING ANALYSIS OF THE CLOCK PERIOD IMPROVEMENT THROUGH CLOCK SKEW SCHEDULING

Statistical static timing analysis (SSTA) methods, which model process variations statistically as probability distribution function rather than deterministically, have been thoroughly performed on traditional zero clock skew circuits. In the traditional zero clock skew circuits, the synchronizing clock signal is designed to arrive in phase with respect to each register. However, designers will often schedule the clock skew to different registers in order to decrease the minimum clock period of the entire circuit. Clock skew scheduling imparts very different timing constraints that are based, in part, on the topology of the circuit. In this paper, SSTA is applied to nonzero clock skew circuits in order to determine the accuracy improvement relative to their zero skew counterparts, and also to assess how the results of skew scheduling might be impacted with more accurate statistical modeling. For 99.7% timing yield (3σ variation), SSTA is observed to improve the accuracy, and therefore increase the timing margin, of nonzero clock skew circuits by up to 2.5×, and on average by 1.3×, the amount seen by zero skew circuits.